Acetabular Labrum

Description

Illustration of the hip joint including the acetabular labrum

3D lateral view of the hip with the femur removed demonstrates a common method for dividing the acetabular labrum into segments.

Normal acetabular labrum. Axial oblique proton-density image (A) and sagittal fat-suppressed T1-weighted image (B) from a magnetic resonance arthrogram show a normal acetabular labrum. On the axial oblique image, the anterior (arrowhead) and posterior (arrow) labrum is uniformly low signal with no contrast tracking into the labral substance; the sagittal image illustrates the normal low-signal anterior–superior labrum (arrow).

Alternative Names

• Acetabular Labrum
• Hip Labrum
• Glenoid labrum of the hip
• Labrum acetabulare

General

• Fibrocartilagenous structure which outlines the acetebular rim
• Covers 170° of femoral head
• Functions: shock absorption, joint lubrication, pressure distribution, stability
• Horse-shoe shaped
• Continuous with the transverse acetabular ligament
• Articular side composed of fibrocartilage, capsular side composed of dense connective tissue

Structure

• Usually triangular in cross-section anteriorly
• More bulbous with square dimensions and a rounded distal edge posteriorly.
• Lecouvet et al: labrum was triangular in cross section in 66% of 200 asymptomatic volunteers
  • Other studies, rounded, flattened, and irregular variants have been identified, particularly in older age groups

Surfaces

• The labrum has three surfaces and an apex
• Articular surface is located internally,
• External surface is in contact with the joint capsule
• Basal surface attaches to the transverse acetabular ligament as well as the bone and hyaline cartilage of the rim of the acetabulum
• The apex of the labrum is a free edge that embraces the head of the femur and forms a seal that enhances lubrication of the joint with synovial fluid.
• Thus the labrum deepens the cup-shaped acetabulum to provide extra coverage for the femoral head

Anatomic Variance

• The dimensions of the labrum are not uniform.
• Seldes et al reported that the widest portion is located anteriorly and the thickest superiorly
• Lecouvet et al found an absence of the labrum in 14% of asymptomatic volunteers

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Function

General

• Acts to increase stability at the hip joint by deepening the acetabulum and resisting lateral and vertical translation of the femoral head.
• Although the labrum deepens the acetabulum by 21%, this stabilizing effect is thought to be less important than the similar function provided by the glenoid labrum because the osseous acetabulum is considerably deeper than the glenoid fossa.
• Provides a seal for the joint, enhancing fluid lubrication, maintaining synovial fluid pressure, and preventing direct contact of the joint surfaces.
• This allows some of the load is borne by fluid pressure and applied forces are distributed more evenly across the articular surfaces.
• Increases the surface area of the acetabulum by 28%

Preventing Hip Osteoarthritis

• The role of the labrum in preventing early osteoarthritis is controversial.
• A labrum-free hip model showed that contact stress increased by 92%
• whereas a biomechanical study measuring contact and pressure distribution in cadaveric joints before and after labral removal showed no significant changes

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Vascular Supply

• Retinacular vessels arising mainly from the superior and inferior gluteal vessels

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Innervation

• Branch of nerve to the quadratus femoris
• Obturator Nerve

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Clinical Significance

Pathology

• Acetabular Labrum Tear
• Hip Osteoarthritis

Procedures

• Hip Paralabral Cyst Aspiration and Injection
• Hip Injection

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See Also

• Hip Anatomy (Main)
• Hip Pain (Main)
• Physical Exam Hip

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